The majority of international trade is shipped in containers that are loaded into the holds of ships at a port of origin and then off-loaded at ports where the shipping containers can be moved by train and truck to the final intended destinations. FIG. 1 illustrates a ship and a gantry crane being used to unload containers from the ship at such a port. There are 10 million containers shipped to the United States annually. As recognized by the 2007 U.S. Federal Government House Resolution 4954, passed into law in 2007, all shipping containers need to be inspected for possible sources of radioactivity, and or radiation shields. However, in reality, Customs and Border Protection (CPB) does not have, and will not be obtaining the resources required to physically inspect all shipping containers entering the U.S. CPB currently randomly selects and inspects only two to four percent of the total containers entering this country. It is perceivable that international terrorist groups will attempt to exploit this vulnerability. The potential risk that containers holding nuclear bombs might be off-loaded from a ship at a foreign port and transported to other locations in this country raises significant security concerns for the nation. Accordingly, it is highly desirable to provide a new technology that can be used to verify the safety of shipping container contents, by detecting nuclear material that might be contained therein.
Radiation detection equipment can be used to detect radioactive materials that are used in nuclear bombs hidden within shipping containers, and steps are being taken to check every shipping container entering this country for such materials. However, it is clear that radioactive materials may not be easily detected with radiation sensors if the radioactive materials are enclosed with lead or other high mass density shielding. Accordingly, it is also desirable to be able to detect objects having relatively high mass density that might be evidence of a shielded nuclear bomb disposed within a container.
Since it would be impractical to open every container passing into and through U.S. seacoast ports for inspection, a detection scheme must be provided for determining when objects with relatively high mass density (that might represent a shielded nuclear bomb) are disposed within a container, particularly when the freight indicated on the manifest listing for the container does not indicate that any such object having a relatively high mass density should be included. In contrast, there should be no problem in searching only containers in which an object of relatively high mass density is detected, and only if there is no corresponding object indicated on the manifest listing, since that combination of circumstances should be uncommon.
FIG. 2 is a schematic diagram 20 that illustrates the relationship between a cargo manifest 22 and objects detected in a container, such as cargo of relatively lower mass density (examples shown are grain, dirt, or other powdered goods 24, and rags, clothing, or brooms 26) which when detected in the container would not likely be cause for inspecting the container. In contrast, cargo of relatively higher mass density (examples shown are chairs, engines, or tools 28) may be cause for inspecting the container. Similarly, if a high mass object is detected in a container that is otherwise empty based on cargo manifest 22, then that container may also require inspection as indicated by a block 30.
Clearly, if based on the manifest listing, a container is supposed to hold high mass density objects, there would be little motive to search a container in which such an object was detected. Moreover, the distribution of mass (i.e., of objects) within the container may provide further clues indicating that something other than the expected contents are included therein. For example a shipment of engine blocks might be expected to be generally uniformly distributed within a shipping container. Yet, if an object with relatively higher mass density than that of the engine blocks was detected in the container, it is likely that a manual search of the container contents would be justified to determine the nature of such an object.
Clearly, a technique for determining the mass density of objects in a container would best be implemented without interrupting the flow of containers being offloaded from a ship or being moved into storage, or onto trucks or rail cars. Accordingly, it would be desirable to detect objects with a relatively high mass density in a container using components that are included in devices employed at a port to move containers, such as the gantry crane shown in FIG. 1. Further, the process for detecting objects with relatively high mass should be carried out substantially without slowing the handling of the containers. These and other desired features and functionality will determine how this monitoring technique might be efficiently implemented.